Isolating Track Segments (UNDER CONSTRUCTION)

This how-to is written based on the use of the old 9V Lego train system. The techniques described here can also be used with 12V Lego trains. RC/PF-trains are subject to a different approach, see also the last chapter of this how-to. This how-to has the following chapters:
1. Isolating track segments
2. Powering isolated track segments

1. Isolating track segments
This is the first chapter of the how-to automating Lego trains and in this chapter I’ll explain how to make a train stop at a certain point in the layout.

To make a train stop at a certain point in the layout, you need to isolate this part and give it a separate power supply. With an isolated track segment, you can cut off the power in that segment without intefering the power supply to the rest of the track. It is wise to make a segment a few track sections (1 section is 16 studs) long: a moving train has a certain momentum (mass x speed) and will not stop at once when the power supply is taken away. Trial and error will tell you how long the isolated segment should be.

A Lego train track is most of the times a loop and in that case, the power is supplied in a loop, see image below.

Full loop power supply

Power supplied in a loop means that if you interrupt the power supply somewhere in this loop, the part next to the cut will still get the power from the other side of the loop, see image below.

Full loop power supply with one interruption

So to make an isolated track segment, you must always have two power interruptions. The part between the interruptions will then be completely isolated and can be connected to another power supply, see image below.

Full loop power supply with two interruptions

To make an interruption, take a good look at the 9V track: every straight and curve track section has a few holes under the rail. See the red arrows in image below.

Holes in straight and curved Lego 9 volt rails

This is where you want to make an interruption by sawing the rail in two. But wait just yet! You need to connect also some wires to the rails to be able to supply the power to the rails. You can do this with the regular rails connectors that come with the 9V speed regulator (part 5306c01), but these wires are quite rare and expensive. A more easy method is to solder on a few wires. And that’s where the hole under the section comes in: you can use it to guide a wire below the section, without having to raise it. See the blue arrows in the image above. It is advised to determine first where you want the wires to be before sawing the rails.

Now you can saw both rails. Sometimes the small last part of the rails at the end will let loose. This is not a problem. It’s even a bit convenient: now you can spot more easily that you’re holding an interrupted track section.

Soldering a wire onto a rail can be a bit difficult: there’s a thin layer of oxide that prevents the soldering tin to attach to the rail. After a while heating and tinning it, the thin layer of oxide disappears and the tin will attach. Also, make sure that you solder on the outer sides of the rails, since the wheels of the train run on the top and inner side of the rails.

The end result should look something like this.

Isolated section Lego 9V straight rail

You can connect the wires to a screw terminal or whatever you prefer. You need two of these interrupted sections to make a fully isolated track segment. You need just one of the two to connect to a power supply, so you have to solder wires to just one interrupted section. The track sections between the two interrupted sections are isolated too and with these you can make your isolated section to the desired length. Note that the minimum length is about one track section if you connect them like in the image below.

Shortest isolation section Lego 9V straight rail

You can also have more isolated segments in one loop. But if you do that, a part of the track that needs to be powered by the regular power supply will be isolated from this power. This is the part between the two isolated segments, the curve on the right in the image below.

Lego train loop with two isolated segments

To solve this problem, you need to bypass one of the isolated track segments. This can be done by using two power regulator wires (5306c01) connected together but this is quite an expensive solution. It’s cheaper to connect the rails by soldering wires between them. In this case you don’t have to cut any rails, just solder a few wires to the rails and make sure that they’re long enough to bypass the whole isolated segment. It’s preferred that you make a bypass close to the power supply. That means that in the above shown layout, you should bypass the lower isolated segment. This way, the current is distributed more equally. See image below.

Isolated segment bypass

The image below shows the end result. It is advised to use two colours for the wires: that way you are sure that you connect the polarity right and prevent eventual unexpected fireworks!

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